.TH IM_DILATE 3 "14 May 1991"
.SH NAME
im_dilate, im_dilate_raw, im_erode, im_erode_raw \- perform morphological operations on a white object against a black background
.SH SYNOPSIS
.B #include <vips/vips.h>

.B int im_dilate(in, out, m)
.br
.B IMAGE *in, *out;
.br
.B INTMASK *m;

.B int im_erode(in, out, m)
.br
.B IMAGE *in, *out;
.br
.B INTMASK *m;

.B int im_dilate_raw(in, out, m)
.br
.B IMAGE *in, *out;
.br
.B INTMASK *m;

.B int im_erode_raw(in, out, m)
.br
.B IMAGE *in, *out;
.br
.B INTMASK *m;

.SH DESCRIPTION
The above functions are applications of morphological operations on one
channel binary images ie. images with pixels that are either 0 (black) or 255
(white).  All functions assume that input images contain white objects against
a black background.

Mask coefficients can be either 0 (for object) or 255 (for background) or 128
(for do not care).

The mask should have odd length sides and the origin of the mask is at location
(m-\>xsize/2,m-\>ysize/2) integer division.  All algorithms have been based on
the book "Fundamentals of Digital Image Processing" by A.  Jain, pp 384-388,
Prentice-Hall, 1989.  Essentially, 
.B im_dilate(3) 
sets pixels in the output if
*any* part of the mask matches, whereas 
.B im_erode(3) 
sets pixels only if *all*
of the mask matches.

.B im_dilate(3)
dilates the image pointed by in, according to the mask pointed by m and writes
the result in the location pointed by the IMAGE descriptor out. The output
image is the same size as the input, in the manner of
.B im_conv(3).

.B im_dilate_raw(3)
works as im_dilate(3), but does not expand the input.

.B im_erode(3)
erodes the image pointed by in, according to the mask pointed by m and writes
the result in the location pointed by the IMAGE descriptor out. Again, the
output image is forced to have the same size as the input.

.B im_erode_raw(3)
works as im_erode(3), but does not expand the input.

See the boolean operations 
.B im_andimage(3), 
.B im_orimage(3) 
and 
.B im_eorimage(3) 
for analogues
of the usual set difference and set union operations.

.SH RETURN VALUE
All functions returns 0 on success and -1 on error.
.SH SEE ALSO
im_read_imask(3), im_conv(3), im_andimage(3), im_rotate_imask(3).
.SH COPYRIGHT
1991-1995, Birkbeck College and the National Gallery